onboard voltage indicator started reading lower under load. Historically, replacing battery and / or alt. has fixed it. Not this time.
Replaced battery, alternator, and replaced the heavy wire connector to the alternator. Meter still running low under load, especially with the A/C on. Lights affect it to a smaller degree. Autozone tested the old alt on a bench. After failing the onboard test (bad voltage regulator), it passed the bench test. New alternator is failing the same test, the same way. Is there a historical classic failure that drives this issue with this model Ford? Or do I just need to follow a logical trouble shooting process to find a new electrical problem. I am fairly dangerous with a volt meter. I have managed to blow up one. I have a nice new amp meter too. Right now, I have to remove the new alternator, and replace it with the old one to get my money back. That will not solve the problem. I need advice on how to move through this to ID the root cause, and make the associated correction.

Found this forum today. I have had my truck since 1999. It is a basic truck, Arizona Bronze, original paint, no rust. Love my truck. Please help me fix it. Inline 6 cyl engine, manual 5 speed transmission, super cab.

Thanks,
George

 

Read up on the G3 alternator upgrade.
I did the "conversion" on my truck "160amp" and haven't looked back since.
I consider it money well spent.

Good Luck

Bob

 

"After failing the onboard test"
What test are you talking about?

Did you change clusters?

 

Autozone ran the charging system through their test procedure using their test equipment.

 

That's 3G, not g3. I think there is a sticky about it in the 80-86 section. Its a good way to go, you can get a cheap alternator, have it tested, then install it and have a better setup.

 

Make sure the light green wire with a red strip has power on at the alternator with the key on.

 

Process instructions (please comment)
1) unplug the d shaped connector.
2) set up a voltmeter to read volts DC.
3) turn the key to the on position.
4) measure the voltage drop from the green/red wire to ground (alternator case)
5) I should see a voltage level. What voltage should I see (12 volts?)

Please confirm. I will report results. I have installed new connectors at the alternator.

Thanks,
George

 

You're right.....corrected now

 

Measured dc voltage on green/red wire with key on. Grounded to multiple places on although. Body and on truck body. Result oscillated quickly from roughly 2 volts to 200 mv. I do not trust this result. Measured voltage over battery truck off. 12.77 volts. Measured voltage over battery with truck on. 14.2 volts. Turned on AC... 13.9 volts. Turned on lights....13.1 volts. Affect seems to be only noticeable after the engine warms up.

 

Read about the 3G conversion. If I have a load issue(that I have not seen previous to last week with a 75 amp alternator) how would th 3G fix that issue? Wouldn't it be affected by the same load change the same way that the 75 amp alternator is affected?

 

Under full load at idle engine warm, measured 13.38 volts. 10 minutes later, measured 13.53 volts. Full load means AC and lights. Do I just need to quit worrying and move on? Or does my truck have a real problem ( variance from 13.1 volts to 13.9 volts under full load at the battery?

 

It appears to be charging just fine. I think I wouldn't worry about it.

 

I'm about to do the 3g myself. If you can find a g3 (HK battle rifle) for the price of a 3g, let me know!

 

After observing my onboard voltmeter for a few days of operation with the new connectors, new battery, and old alternator (11yrs old btw aftermarket brand from Autozone, do you believe it?) The low voltage reading appears to have slowly gone away, occuring a few times after the install, but has not happened in the last 3 days. No need for a 3G alternator at this time. Thanks for the advice. Now, I have to replace a fuel pump and fuel filter.

George